Minor fixes/simplifications to time functions

* doc/lispintro/emacs-lisp-intro.texi (Files List): Simplify.
* doc/lispref/os.texi (Time of Day): Mention format-time-string
as an alternative to current-time-string.
* lisp/arc-mode.el (archive-unixdate, archive-unixtime):
Port better to future versions of Emacs where (COUNT . HZ)
will take precedence to (HI . LO).
* lisp/arc-mode.el (archive-unixtime):
* lisp/calendar/todo-mode.el (todo-insert-item--basic)
(todo-item-done, todo-read-time):
Prefer format-time-string to substringing current-time-string.
* lisp/calc/calc-forms.el (calc-time, calcFunc-now):
Prefer decode-time to parsing the output of current-time-string.
* lisp/emacs-lisp/cl-extra.el (cl--random-time):
Prefer encode-time to hashing the output of current-time-string.
* lisp/gnus/gnus-score.el (gnus-score-headers)
(gnus-score-adaptive):
Avoid stringifying and then reparsing timestamp.
* src/timefns.c (Fencode_time): Omit redundant assignment.

5 files changed, 19 insertions, 26 deletions

diff --git a/lisp/arc-mode.el b/lisp/arc-mode.el
index 068702bc71b..9d63a2a579a 100644
--- a/lisp/arc-mode.el
+++ b/lisp/arc-mode.el
@@ -637,7 +637,7 @@ the mode is invalid.  If ERROR is nil then nil will be returned."
 
 (defun archive-unixdate (low high)
   "Stringify Unix (LOW HIGH) date."
-  (let* ((time (cons high low))
+  (let* ((time (list high low))
          (str (current-time-string time)))
     (format "%s-%s-%s"
             (substring str 8 10)
@@ -646,8 +646,7 @@ the mode is invalid.  If ERROR is nil then nil will be returned."
 
 (defun archive-unixtime (low high)
   "Stringify Unix (LOW HIGH) time."
-  (let ((str (current-time-string (cons high low))))
-    (substring str 11 19)))
+  (format-time-string "%H:%M:%S" (list high low)))
 
 (defun archive-get-lineno ()
   (if (>= (point) archive-file-list-start)
diff --git a/lisp/calc/calc-forms.el b/lisp/calc/calc-forms.el
index f7586288ca2..ccd52d370d1 100644
--- a/lisp/calc/calc-forms.el
+++ b/lisp/calc/calc-forms.el
@@ -37,13 +37,11 @@
 (defun calc-time ()
   (interactive)
   (calc-wrapper
-   (let ((time (current-time-string)))
+   (let ((time (decode-time)))
      (calc-enter-result 0 "time"
                         (list 'mod
                               (list 'hms
-                                    (string-to-number (substring time 11 13))
-                                    (string-to-number (substring time 14 16))
-                                    (string-to-number (substring time 17 19)))
+                                    (nth 2 time) (nth 1 time) (nth 0 time))
                               (list 'hms 24 0 0))))))
 
 (defun calc-to-hms (arg)
@@ -1341,16 +1339,15 @@ as measured in the integer number of days before December 31, 1 BC (Gregorian)."
           (math-parse-iso-date-validate isoyear isoweek isoweekday hour minute second)))))
 
 (defun calcFunc-now (&optional zone)
-  (let ((date (let ((calc-date-format nil))
-                (math-parse-date (current-time-string)))))
-    (if (consp date)
-        (if zone
-            (math-add date (math-div (math-sub (calcFunc-tzone nil date)
-                                               (calcFunc-tzone zone date))
-                                     '(float 864 2)))
-          date)
-      (calc-record-why "*Unable to interpret current date from system")
-      (append (list 'calcFunc-now) (and zone (list zone))))))
+  (let ((date (let ((now (decode-time)))
+                (list 'date (math-dt-to-date
+                             (list (nth 5 now) (nth 4 now) (nth 3 now)
+                                   (nth 2 now) (nth 1 now) (nth 0 now)))))))
+    (if zone
+        (math-add date (math-div (math-sub (calcFunc-tzone nil date)
+                                           (calcFunc-tzone zone date))
+                                 '(float 864 2)))
+      date)))
 
 (defun calcFunc-year (date)
   (car (math-date-to-dt date)))
diff --git a/lisp/calendar/todo-mode.el b/lisp/calendar/todo-mode.el
index 41fe57e60ce..145cf78e6de 100644
--- a/lisp/calendar/todo-mode.el
+++ b/lisp/calendar/todo-mode.el
@@ -1931,7 +1931,7 @@ their associated keys and their effects."
                              (calendar-current-date) t t))))
              (time-string (or (and time (todo-read-time))
                               (and todo-always-add-time-string
-                                   (substring (current-time-string) 11 16)))))
+                                   (format-time-string "%H:%M")))))
         (setq todo-date-from-calendar nil)
         (find-file-noselect file 'nowarn)
         (set-window-buffer (selected-window)
@@ -2881,8 +2881,7 @@ visible."
              (not marked))
       (let* ((date-string (calendar-date-string (calendar-current-date) t t))
              (time-string (if todo-always-add-time-string
-                              (concat " " (substring (current-time-string)
-                                                     11 16))
+                              (format-time-string " %H:%M")
                             ""))
              (done-prefix (concat "[" todo-done-string date-string time-string
                                   "] "))
@@ -6091,7 +6090,7 @@ the empty string (i.e., no time string)."
     (while (not valid)
       (setq answer (read-string "Enter a clock time: " nil nil
                                 (when todo-always-add-time-string
-                                  (substring (current-time-string) 11 16))))
+                                  (format-time-string "%H:%M"))))
       (when (or (string= "" answer)
                 (string-match diary-time-regexp answer))
         (setq valid t)))
diff --git a/lisp/emacs-lisp/cl-extra.el b/lisp/emacs-lisp/cl-extra.el
index 13988db9a86..78484fcfa3f 100644
--- a/lisp/emacs-lisp/cl-extra.el
+++ b/lisp/emacs-lisp/cl-extra.el
@@ -438,9 +438,7 @@ as an integer unless JUNK-ALLOWED is non-nil."
 ;; Random numbers.
 
 (defun cl--random-time ()
-  (let* ((time (copy-sequence (current-time-string))) (i (length time)) (v 0))
-    (while (>= (cl-decf i) 0) (setq v (+ (* v 3) (aref time i))))
-    v))
+  (car (encode-time nil t)))
 
 ;;;###autoload (autoload 'cl-random-state-p "cl-extra")
 (cl-defstruct (cl--random-state
diff --git a/lisp/gnus/gnus-score.el b/lisp/gnus/gnus-score.el
index 327cc69392d..f777163cc31 100644
--- a/lisp/gnus/gnus-score.el
+++ b/lisp/gnus/gnus-score.el
@@ -1501,7 +1501,7 @@ If FORMAT, also format the current score file."
       (when (and gnus-summary-default-score
                  scores)
         (let* ((entries gnus-header-index)
-               (now (date-to-day (current-time-string)))
+               (now (time-to-days (current-time)))
                (expire (and gnus-score-expiry-days
                             (- now gnus-score-expiry-days)))
                (headers gnus-newsgroup-headers)
@@ -2380,7 +2380,7 @@ score in `gnus-newsgroup-scored' by SCORE."
                (memq 'word gnus-newsgroup-adaptive))
       (with-temp-buffer
         (let* ((hashtb (gnus-make-hashtable 1000))
-               (date (date-to-day (current-time-string)))
+               (date (time-to-days (current-time)))
                (data gnus-newsgroup-data)
                word d score val)
           (with-syntax-table gnus-adaptive-word-syntax-table